A new DOOM 3 Q&A has been posted on PC.IGN. id Software CEO Todd Hollenshead is asked about the game's concept, environments, weapons, A.I., interactivity and the lack of co-op on the PC.
With respect to the environments, they're really hyper-realistic in nature in terms of the indoor environments within the UAC facility. Because you're on Mars, there's no atmosphere, so there's not a lot of opportunity for you to go outside, but you do get to see what the landscape of Mars looks like outdoors. There are some limited missions where you spend some limited time outside, but because of a limited air supply, you're not roaming the surface of the planet, because it's barren and there's not a lot to do there and the demons are taking over the base anyway, so you sort of would be wandering aimlessly.